The present invention relates to power supplies and, more particularly to, switching power supplies.
Power supplies are a common feature in electrical hardware and are used to process a source power into a more usable form, with voltage and current levels compatible with the electrical circuitry, termed the "load" to which they are connected. Typically such processing includes voltage current transformation, output voltage stabilization and electrical line load isolation.
A particular component of the power supply is the transformer which not only converts the input power from typical source voltage and current levels to a transformed output power at a transformed output voltage and current level but also electrically isolates the load from the supply lines.
However, transformers have the disadvantage of being intrinsically incapable of continuous operation. Typically the discontinuity in their operation is compensated for by the addition of energy storage circuits, that is "filters", on the power supply outputs. The term "filter" is drawn from the fact that they filter out the AC component or "ripple" out of the power delivered to the load.
Developments in power supplies have resulted in switching power supplies that operate at frequencies independent of and often much higher than their input power line frequencies. This is in part due to the fact that such higher operating frequencies result in the use of cheaper and smaller components. However, such reductions are not as pronounced in some high frequency switching power supplies, particularly those adapted for high current low voltage power production.
Further developments particularly in high power units have led to switching power supplies in which voltage regulation is performed prior to the transformers and, the transformer is used in a near continuous fashion by operating it in a bi-directional mode. This leads to further, moderate size and cost reductions in the output filters, with low voltage or high current filters once again benefitting least.
However, switching power supplies that utilize their transformer in a bi-directional fashion suffer from several disadvantages. Firstly, the control circuits must guarantee that its operation is balanced, or else the average core flux will become non-zero, and if left unchecked will proceed towards a saturation limit. Secondly, where near continuous operation is the goal the control circuits must simultaneously attempt to minimize the duration of the "change-over" gap while insuring that no overlap occurs, since any overlap can easily lead to a catastrophic circuit failure. Lastly, in low voltage, high current power supplies, the conventional two turn, center tapped secondary is mechanically difficult, clumsy and expensive due to the thickness and stiffness of the wire used.